


Invaluable Ingredients

by razielim



Series: Merry Smutmas 2017 [12]
Category: Voltron: Legendary Defender
Genre: Alternate Universe, Alternate Universe - Merpeople, Anal Sex, Gigantic Dick, M/M, Mild Blood, Orca Mer!Shiro, Underwater Sex, Wizard Keith, extreme penetration
Language: English
Status: Completed
Published: 2017-12-25
Updated: 2017-12-25
Packaged: 2019-02-11 19:23:23
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,906
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12942015
Author URL: https://archiveofourown.org/users/razielim/pseuds/razielim
Summary: Merry Smutmas, ilovelocust!The vial of potion was hot in his tightly clenched hand. He could see Shiro already beached, rolling idly in the sand, waiting for him. Shiro didn’t know yet that today was going to be a fun day.





	Invaluable Ingredients

He could see Shiro already beached, rolling idly in the sand and waiting for him.

Keith picked up the pace as he skidded down the last patches of flattened grass and climbed onto a warm dune, the sand sliding under him.

Keith clutched the potion in his pocket, checking that it hadn’t escaped on his walk from the town. It had taken the whole morning to cure it properly, but the pricetag was much more prohibitive than the process of it. Dolphin spleen of all things… Keith would have to tighten his belt until next March. At the very least.

Over the last dune, he hailed Shiro, who flipped onto his stomach and watched Keith’s approach with his chin in his hands. His tail fanned in the air behind him as he slowly tipped it back and forth, back and forth, a mesmerizing iridescence running over it in scribbles that resembled sunlight dancing on a sea floor.

Keith beamed as he approached. “I have a surprise for you.”

Shiro, who had been watching him with a smile, cocked his mouth to one side as he considered Keith, looking him up and down for a clue. “Am I going to like the surprise?”

Keith frowned. “I don’t know, actually,” he replied, pulling the vial out from his pocket and peering at the aquamarine liquid inside. “Do you like underwater sex?”

Shiro sprang up, as much as a beached merman was able, body propped up on straight arms, suddenly very interested in Keith’s potion. “I thought you said it was too expensive to acquire all the ingredients?” he said, peering at it with a squint.

“I took out a loan,” Keith said. “I figured I deserved to treat myself on my birthday.”

Shiro laughed delightedly and looked up at the sky as if he might be able to see the stars out in the daylight and check the date. Not that merfolk had any skill with reading the skies or keeping track of calendars. “Happy birthday. Though with that kind of price, I’m surprised you didn’t wait for _my_ birthday, since I’m the one that’s been asking for this.”

Keith came forward the last few feet and sat down in the sand. “Yeah, well. I’m happy to make you happy,” he said, letting Shiro take the vial from him and study it. “Besides, I was hoping that if I made this, maybe you might get me the present that _I’ve_ been hoping for.”

“Hm?” Shiro turned to him curiously. He took one look at Keith’s raised brows, and his face immediately fell. Then he frowned at the bottle. “Keith, are you certain? I’m really not sure about that. If I hurt you — ”

Keith nudged Shiro’s bicep with his shoulder, curling into him, his heated gaze sinking from Shiro’s handsome face down to his chest before resurfacing at his eyes. “I’m more than capable of putting a stop to things if it hurts too much.”

Shiro looked back at him again, squinting as the sun finally came out from behind the clouds for the first time that day. “You promise you’ll mind how much pain you’re in?”

“Promise.”

Shiro sighed, long and heavy, and then finally passed the vial back with an indulgent smile. “You’re a menace, Warlock Keith.”

Threading his fingers through Shiro’s around the vial, Keith leaned in and kissed him, soft and sweet and apologizing for all the menacing he’d ever gotten up to while trying to get what he wanted.

✘✘✘✘✘✘✘

They had stashed his robes somewhere safe from wind and waves and swum out quite a bit away where Keith took the potion in one swallow. Shiro led the way through the crystalline sky-blue waters along the shore, past the seaweed line, and into wide open ocean as the sea floor dropped out to heavy depths below them. They came to a cave set into a distant rock formation that sat, rough and scraggly, in what looked to be a rather intimidating part of ocean. Everywhere, basalt formations spoke of danger to soft human skin, and at the depth they were at, Keith was starting to feel a chill. In the corner of his vision, he thought he saw the tail of a shark slash through seaweed, but when he turned to look, there was nothing there.

The effects of the potion had felt weird for a while, and then all at once, breathing water had felt no different than breathing air, though colder than the August weather they'd left behind.

Shiro took his hand to guide him when Keith fell behind, pulling him through an entrance that turned out to only appear shallow when camouflaged against the surrounding rock. Then the cave opened out, and Keith gasped a bit when he saw how bright and lively things were inside. Shiro had many small, bright fish dancing through his living space, swimming in startled bursts between the walls. Shafts of sunlight, coming in through fissures in the ceiling, refracted through crystals and danced in rainbows across their scales. Various flowering weeds covered the walls, all sleepily trailing soft tendrils and petals through the hushed water.

Shiro led him to the bed, which was a sort of concave rock formation covered in a thick mattress of braided seaweed. It squished under him with surprising springiness as Keith sank down onto it.

He’d just barely finished taking in the broadest strokes of the room’s details when Shiro covered Keith’s body with his own, his left hand coming to rest possessively on Keith’s waist. He kissed Keith with the slow intensity that was always the prominent disposition of his kisses.

They kissed for a long time, Keith lost in the sounds of their moaning. Each sound he or Shiro made vibrated so thickly through the water between them that it was like having his ear pressed directly to someone’s throat — sensual to a near deafening degree.

It made communicating difficult, syllables exploding over each other in confusing echoes, and Keith had given up talking almost immediately upon submerging.

As Shiro kissed him, leading him into an adventure of pull and nip and duck and play, gripping Keith firmly by his biceps, Keith slipped his knee up to rub against the front of Shiro’s tail — that place where the skin was the slightest bit spongier than the surrounding blubber and muscle. He rubbed until he felt Shiro’s cock start to breach the slitted opening, swelling in size and looking for escape, and then wrestled an arm free of Shiro’s grip to continue pressing and coaxing with the butt of his palm.

The cock sprang free into his waiting hand half-hard but already larger than human proportions, and Keith stroked it enthusiastically, getting it ready for what he wanted, chuckling as Shiro moaned up a storm all around them, finally breaking off the kiss and kissing over Keith’s ear and up and down his neck.

The flesh in his hand swelled until he needed a second hand to help him envelope the girth, and Keith carefully tipped Shiro onto his side and then over on his back in the bed, climbing up to straddle his lover’s massive tail.

Then he sank his mouth down to the smooth flesh of Shiro’s dick, sucking and licking at it as best he could, Shiro’s moans rolling out louder.

It wasn’t easy, pleasuring a lover of such dimensions — his mouth could never cover enough territory, and his hands had their job cut out for them, trailing over and over that excessive length.

The biggest surprise of his underwater spelunking came when Shiro started secreting his precome and Keith found that it very much did not dissipate in the water as he had assumed it would. The precome, usually very stringy above water, hovered in a neat bead that stayed attached to the flared head and swelled. Keith pulled his mouth from where it had been sucking the underside of Shiro’s cock to watch it waver and glisten in the water like a soap bubble.

His eyes met Shiro’s amused gaze on the other side of the cocktip and he reached forward, curious. The viscous texture of it latched on to Keith’s fingertips, and as he pulled his hand away, it stretched between Shiro’s dick and his fingers without any signs of pulling apart from either any time soon.

Fascinated, Keith rubbed his fingers against his thumb to feel the texture of it and was surprised to find that it was just as thick and blubbery as it was on land.

Shiro reached a hand out and pressed down on the precome that was continuing to swell and bead on his flat head, using his whole palm to spread it down over the side.

It smeared easily and clung, gelatinous and fuzzy on the edges like it might dissipate at any time, but when Keith reached out to stroke Shiro, he found that the appearance was deceiving and the substance remained just as thick.

Shiro was giving him a heated look, and Keith wondered how long Shiro had wanted to push inside him but been restrained by his sense of danger.

Keith reached behind himself with his hand still trailing merman lubricant which left behind translucent wisps on the hairs of his thigh as it brushed past. It took him a few moments to get his rim to open to his fingers, the chill in the water setting his muscles to clamp tightly. He forced himself to relax enough to admit just the very tips of two fingers, but could get no further.

After all this effort to get Shiro to agree to fuck him, how was he going to fit the massive, blunt cock sitting in front of him if he didn’t find a way to relax? He glanced at the flared cockhead warily, eyeing its spongy little ridges that trailed in soft bumps along the crown, and his mouth watered. At the same time, his rim let his knuckles slip in.

Keith grinned.

Cold or not, his body knew what it wanted.

Shiro sat up, his own sticky hand also trailing precome through the water as he reached under Keith and massaged his perineum, brushing against Keith’s fingers now and then. Eyes growing darker as his pupils blew out, he pushed forward and slipped one and then two fingers right in along with Keith’s, stretching him to a blessedly thick diameter. Keith’s moan hummed through the water, startling away a school of fish that had gotten too close.

Shiro’s much thicker fingers pulled at his rim, testing the limits of the muscle, even as he watched Keith’s face with an intensity that seemed to note every twitch and shudder, judging what was too much and what was just right.

They’d done this before, never in the water, working against the chill, but they’d done this, and despite being pleased that Shiro cared, Keith wished he wasn’t so worried.

Keith pulled his own fingers out, letting Shiro take over, and reached for Shiro’s cock, sliding around more of the precome that was still bubbling up. Eyeing it, he wondered how much of the length would go inside. He supposed he’d just start with the narrower top half, before the medial ring, and worry about the rest later. It probably wouldn’t matter to Shiro how much of it Keith could handle, even just the tip would be as much as Keith could do with his mouth and both hands.

Shiro was fucking him in earnest with all four fingers now, knuckles and fingertips distending Keith’s asshole in all the best ways, his thumb pressing on Keith’s taint, and Keith reached out to halt him.

Their eyes met, and Shiro still looked worried, unsure that Keith was prepared enough. Keith leaned down, nipped at Shiro’s top lip, nipped at his chin, kissed his chest, and then ran the tip of his nose along Shiro’s clavicles, slowly, back and forth, all the while easing Shiro’s hand out of him and massaging his own rim one last time. He opened his eyes and lifted his head, humming contentedly to reassure Shiro that this was exactly what he wanted.

Then he pulled Shiro’s heavy cock up off where it was resting just over Shiro’s lower ribs and lined it up against where his rim was again contracting and flexing in the cool water.

He slid it in edgewise, trying to trick his rim to accepting the taper of the ruffles around the head first, before tackling the whole surface of the blunt tip, letting the weight of the ocean gently press his body down on it without straining too much and risking accidentally clenching.

With an obscene popping sensation and a lurch, the head was swallowed by his body and the sensation was so huge and surprising that Keith pushed it back out immediately. Shiro jerked up, eyes alarmed, hands hovering to assist without knowing how to help, but Keith waved him off, chuckling at the challenge, and tried again.

This time, when the head sprang past the muscle, he stayed loose enough to keep it there, immediately bearing down to build on his progress and make it harder for his body to accidentally reject it again.

His ass slid easily onto the lubricated dick, and the sudden swell of sensation inside him halted him. Keith stopped to stare at Shiro.

The size of it wasn’t as scary as how facile it was, and Keith groped around under himself to find that the medial ring was only four finger widths out, meaning he’d taken half of the length leading up to it.

He shuddered, ass again clenching as the sensation of fullness sparked arousal up his chest, across his ribs, and back down his spine in great big welding arcs.

And before his now tightly squeezing rim could do anything to the contrary, he let his legs relax and sank further, smoothly descending onto Shiro’s cock and feeling it brush up through and to the front of his body. Keith thought he saw an outline of the cockhead just barely ghost through his skin before the sensation of the medial ring distracted him and he looked up at Shiro in a daze.

Shiro looked undone and ready to choke with pleasure. His fingers were dug into the seaweed mattress and his brows were drawn as he stared intently at the place where dick met rim. Keith realized that Shiro’s hips were starting to buck, but he was precariously controlling them to a measured tilt that pushed his medial ring in a teasing bump, bump, bump against Keith’s stubbornly resistant rim.

It was probably flirting with danger to take it, but Shiro’s expression of bewilderment and desperation was too tempting. Keith wanted to see how wrecked Shiro would be if he finally got that deep into his lover after a two year span of being afraid to hurt him.

So, taking a deep breath and letting it out, he sat down hard on the exhale.

With a popping feeling just as lewd as when he’d fit the head in, the medial ring slid into him and sent Keith into a senseless convulsion, his brain fried and nerves cross-wired for a moment. When he finally got his vision sorted, he found Shiro looking up to him, eyes holding a sort of fear and reverence in them.

Keith chuckled softly, and leaned forward, asking for a kiss that was awarded to him with great fervency as Shiro seemed to try to both thank him and fret over him.

Keith rolled his hips to come off the ring, and the pop of it had him shuddering again. Shiro broke off the kiss with a pained moan, wearing an expression of disbelief that Keith took to be a good thing.

And then he forced himself down on the ring once more. He rolled his hips again and again, moaning and shuddering and shaking at the feeling of that delicious, deviant distension in his stretched rim.

He wished he could let Shiro know that it didn’t hurt at all, doubly so when there appeared a faint cloud of blood between them and Shiro gripped Keith’s thighs immediately, stopping his motion and watching the blood in fear.

Keith frowned at it. That hadn’t happened to him in a while, but it was hardly surprising. Pulling off Shiro’s dick, he saw a thin strip of blood mixed into the precome that still clung to Shiro’s dick protectively. He gave Shiro a wry smile and waved his hand. “It’s fine,” he said, but the words were distorted and reverberated horribly.

Shiro still looked worried, but Keith wasn’t about to let such a small thing ruin his good time.

Hovering over the head again, he sank down once more, relishing the return of the heat after having his hole exposed to the cold water. His rim swallowed the tip of the dick with no difficulty this time and Keith smirked as he slid down and watched Shiro’s eyes roll back at the seemingly never-ending thrust. Keith came up to the ring and passed it easily, his stomach feeling full again, and this time he placed a hand there and definitely felt it brush past.

Feeling bold and reckless and incredibly thirsty for more, Keith didn’t stop, and Shiro’s eyes fluttered as Keith sank another couple inches past the ring until his body stopped him, offering painless but unyielding resistance. He tried a couple times this way and that to go further, but there was no negotiating with whatever sphincter had decided he’d had enough.

Keith groaned in frustration — there was still more dick available to sink down on — but rolled his hips anyway, clenching around Shiro, the medial ring perfectly positioned within him to roll over his prostate with every shallow thrust. Keith moaned, finally getting off his feet and kneeling as he fucked himself and jerked off.

Shiro gazed up at him like Keith had hung the moon. His hands came to rest on Keith’s hips and guided him into a faster rhythm, hips tilting up for that extra bit of heavy press at the end of each thrust.

Keith couldn’t stop moaning and yet couldn’t even hear himself over the mess of groans slipping from Shiro as his lover closed his eyes and lost himself to the sensation.

There was a shift of a shadow in the corner of Keith’s eye, and for a second he excused it as a school of fish, and then every hair on his body stood on end, and he turned to find himself face to face with a large grey shark swimming through the cave right at them.

Keith screamed and jerked, and the next moment there was a horrible rattling screech — he turned to find Shiro looking like something from a nightmare, fangs extended and eyes glowing yellow and —

Then the shark was gone, leaving behind it only a lingering sense of exposure and violation.

Keith turned to look at Shiro again, but his lover’s face had returned to normal, leaving behind a furious expression. Something floating in the water between them caught Keith’s eye and he focused on it to see that it was another rusty cloud of dissipating blood droplets.

That explained what had attracted the shark, though it didn’t make him feel any less nervous about sitting in a cave that was exposed to such danger.

Keith went to move off Shiro’s cock, but found himself held tightly in place by Shiro’s hands, retractable claws still out.

Shiro turned to face him and looked him up and down. Then, with a sudden leer, flipped their positions on the bed, spinning Keith around as he went so that all of Keith’s insides gave a confused, twisting lurch.

Merfolk were famous for their sudden humors and unpredictable bouts of mischief in response to unpleasant situations.

Shiro’s mood swings were rare. And yet, suddenly, Keith found himself getting fucked roughly from behind, half kneeling, half floating in the water, propelled up by the violently stirred-up water, and he wondered if he’d been missing out by not seeing more of Shiro’s bestial instinct.

Certainly, Keith thought, as Shiro suddenly broke past the barrier Keith had hit earlier and slid in further than Keith had ever been breached, he’d been missing out by not being able to afford this potion earlier, because getting fucked to gelatin in near weightlessness was its own kind of miracle.

He let himself get lost in the pounding, the head and the ring rolling through his insides and churning him into a boneless, whimpering mess. When he first felt the front of Shiro’s tail slapping his asscheeks, he nearly gagged, having not realized how deep into him Shiro had gotten but now feeling like everything inside his chest cavity was being jostled with each and every thrust.

When he came, fist flying furiously over his dick, it was with wild bursts of technicolored and white stars in his vision before everything washed out into an inky black. Relentless shudders rolled through him as his insides clenched over Shiro’s last thrusts.

He sagged, the roiling water around them calming as Shiro shivered behind him, his hands shaking in their white-knuckled grip on Keith’s hips.

Keith sighed as he dug his fingers into the braided seaweed below and started to pull himself forward and off Shiro with shaking biceps, his legs useless and lifeless somewhere behind him.

The medial ring and then the head each slipped out of him with barely a ripple rolling through his defeated and loose muscles, and not even the sudden flood of cold water in him could shake him out of his near-comatose state, as he floated the rest of the way down to the seaweed and blessedly passed out.

✘✘✘✘✘✘✘

Keith still could walk.

Or he could, probably, if he really tried, but his legs were shaky every time he tried to move them. Shiro had had to pull him all the way to shore, snarling at any and all sharks that wandered too close in their curiosity, and then had to drag him under one arm all the way out of the tide into the soft dunes where Keith now lay on Shiro’s stomach to keep sand away out of his still less-than-continent hole.

“How much potion do you have?” Shiro asked, watching seagulls wheel through the air.

Keith shrugged, thinking he was about to fall asleep again. “Enough for about a month.”

“Hm. I might have to go looking for sunken treasure in that case. So you can afford more.”

Keith smiled lazily, rubbing his face into the warm skin of Shiro’s chest. “So I’ll take it you have no more reservations about letting me on your dick?”

Shiro laughed. “To be honest, it’s a relief to know it’s possible. Still, I’d rather we do something about the bleeding.”

Keith shuddered. “Yeah, I’m going to have nightmares about that shark.”

“It would also be nice to talk underwater.”

“I guess I have my work cut out for me. Just don’t complain that I’m spending more time digging through library potion recipes than riding your dick.”

“Oh.” Shiro paused, his hand that wasn’t coated in sand slipping down to toy with Keith’s hole. “Hm. Maybe those things will have to wait. I’m not about to miss out on hearing you moan if I can more or less figure out what the moans mean.”


End file.
